Sealant composition for liquid crystal and process for producing liquid-crystal display panel with the same

ABSTRACT

The present invention provides a liquid crystal sealing composition and a liquid crystal display panel excellent in adhesion, moisture permeation resistance and heat resistance and superior for use in a sheet press heating bonding system. The liquid crystal sealing composition comprises (1) an alkoxysilyl group-containing modified epoxy resin obtained by de-alcohol condensation reaction of (a) an epoxy resin having at least one hydroxyl group in one molecule and (b) an alkoxysilyl group-containing compound, (2) a heat latent epoxy curing agent, (3) a filler having an average particle diameter of 0.1 to 10 μm, and if necessary (4) an epoxy resin having at least 1.2 epoxy groups on average in one molecule, (5) an aprotic solvent having a boiling point in the range of 140 to 220° C., compatible with epoxy resin and inert to an epoxy group, and (6) other additives.

TECHNICAL FIELD

The present invention relates to a sealing composition for liquidcrystal display panel, which is excellent in adhesion, moisturepermeation resistance and heat resistance, a method of producing aliquid crystal display panel by using the same, and a liquid crystaldisplay panel.

BACKGROUND ART

In recent years, liquid crystal display panels characterized by lightweight and high accuracy came to be widely used as display panels forvarious devices including cellular phones. As the use of the liquidcrystal display panels is diversified, the environment where they areused is becoming strict. Further, liquid crystal display cells are alsorequired to be highly accurate and uniform with high qualities.

A liquid crystal sealing composition is used to seal liquid crystalsencapsulated between transparent glass substrates or plastic substratesprovided suitably with transparent electrodes and an orientation filmimportant as members constituting a liquid crystal display panel, sothat the liquid crystals will not leak to the outside. In this sealingcomposition, an epoxy resin-based the heat cured resin composition ofone-component type is widely used.

Small liquid crystal panels including cellular phones and display panelsfor car navigation are used outdoors or in automobiles, thus requiringimprovements in impact resistance and resistance to high temperature andhigh humidity, and the liquid crystal sealing composition also stronglyrequires improvements in adhesion and heat resistance.

Generally, techniques of improving the adhesion of the heat cured epoxyresin compositions involve adding a large amount of rubber-likecomponents such as CTBN, ATBN and ether elastomers or epoxy resincomponents modified with the rubber-like components in order to improvestress relaxation and adhesiveness. In this case, however, the glasstransition temperature (Tg) of the resulting cured product is low due tothe influence of the Tg of the rubber-like components, thus making heatresistance insufficient.

To improve the heat resistance of the epoxy resin composition used inthe liquid crystal sealing composition, there is also a method of mixinga large amount of fillers such as glass fibers, glass particles andamorphous silica. In doing so, heat resistance is improved, but theresulting cured product tends to be brittle to lower adhesiveness.

In a production site for liquid crystal display panels, there is a trendthat the time in a heating bonding step is reduced in order to improvethe productivity of more uniform and high-quality liquid crystal displaypanels. From the viewpoint of productivity, a system for siamese heatingpress bonding of a plurality of plates is recommended and widelypracticed. The system for siamese heating press bonding of a pluralityof plates is a system wherein plural pairs of liquid crystalcell-forming substrates, one substrate of which is coated with a liquidcrystal sealing composition, are layered, pressed under vacuum andthermally bonded in a heating furnace to produce liquid crystal displaypanels. A sheet press heating bonding system wherein a pair oftransparent substrates for liquid crystal cell is sealed one afteranother by heat press bonding.

For this sheet press bonding system, for example, JP-A 10-273644proposes a liquid crystal sealing composition comprising (a) liquidepoxy resin, (b) a curing agent consisting of novolak resin having asoftening point of 75° C. or less as determined by a ring and ballmethod, (c) a filler having a particle diameter of 10 μm or less and (d)a curing accelerator as essential ingredients, wherein a mixture of thecomponents (a) and (b) is liquid or has a softening point of 50° C. orless as determined by a ring and ball method. When the epoxy resincomponent and the curing agent component are in the form of liquid orhave such low softening point, the composition undergoes rapid reductionin viscosity in a the heat cured step in the sheet press heating bondingsystem, thus easily bringing about a phenomenon such as burnout in aseal form or foaming in the seal. Further, the glass transitiontemperature of the cured liquid crystal sealing composition tends to belowered to deteriorate heat resistance.

JP-A 2001-64483 proposes a sealing composition for liquid crystaldisplay panel, which comprises epoxy resin, a curing agent, epoxylatedpolybutadiene and an inorganic filler. In this publication, theepoxylated polybutadiene component is essential. This sealingcomposition is excellent in retention of seal shape in the sheet pressheat bonding system, but the glass transition temperature of theepoxylated polybutadiene component is low, and thus the glass transitiontemperature of the cured liquid crystal sealing composition is alsolowered, thus easily deteriorating heat resistance.

Accordingly, the object of the present invention is to provide a novelliquid crystal sealing composition which is compatible with the sheetpress heating bonding system, can demonstrate high-speed production andis superior in cell adhesion, moisture permeation resistance and heatresistance.

DISCLOSURE OF INVENTION

To solve the problem described above, the present inventors madeextensive study, and as a result they found that the problem can besolved by the following liquid crystal sealing composition, and thepresent invention was thereby completed.

That is, the liquid crystal sealing composition of the present inventioncomprises (1) analkoxysilyl group-containing modified epoxy resinobtained by de-alcohol condensation reaction of (a) an epoxy resinhaving at least one hydroxyl group in one molecule and (b) analkoxysilylgroup-containing compound, (2) a heat latent epoxy curing agent, (3) afiller having an average particle diameter of 0.1 to 10 μm, and ifnecessary (4) an epoxy resin having at least 1.2 epoxy groups on averagein one molecule, (5) an aprotic solvent having a boiling point in therange of 140 to 220° C., compatible with epoxy resin and inert to anepoxy group, and (6) other additives.

The method of producing a liquid crystal display panel according to thepresent invention comprises the heat cured above-described liquidcrystal sealing composition in a liquid crystal sheet press heatingbonding system.

The liquid crystal display panel of the present invention ischaracterized in that it is produced by the liquid crystal display panelproduction method described above.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the liquid crystal sealing composition used in the presentinvention is described in more detail.

Specifically, the liquid crystal sealing composition of the presentinvention comprises (1) an alkoxysilyl group-containing modified epoxyresin obtained by de-alcohol condensation reaction of (a) an epoxy resinhaving at least one hydroxyl group in one molecule and (b) analkoxysilyl group-containing compound, (2) a heat latent epoxy curingagent, (3) a filler having an average particle diameter of 0.1 to 10 μm,and if necessary (4) an epoxy resin having at least 1.2 epoxy groups onaverage in one molecule, (5) an aprotic solvent having a boiling pointin the range of 140 to 220° C., compatible with epoxy resin and inert toan epoxy group, and (6) other additives. Now, these components arespecifically described.

(1-1) Alkoxysilyl Group-Containing Modified Epoxy Resin

(a) Epoxy resin having at least one hydroxyl group in one molecule

The epoxy resin is not particularly limited insofar as it is one kind ofepoxy resin satisfying the above requirement. Examples include bisphenolepoxy resin, carboxylic acid-modified epoxy resin, and glycidyl group-and hydroxyl group-containing radical copolymers, etc.

[Bisphenol Epoxy Resin]

The bisphenol epoxy resin is represented by the following formula (1):

wherein R₁ and R₂ each represent a methyl group or a hydrogen atom, n isthe number of repeating units, and when the bisphenol epoxy resincontains a resin wherein n is 1 or more, a considerable amount of theresin wherein n is 0 may be contained. Specific examples of thebisphenol epoxy resin include bisphenol A epoxy resin, bisphenol F epoxyresin, bisphenol AD epoxy resin etc. Hydrogenated products of thebisphenol epoxy resin can also be preferably used.[Carboxylic Acid-Modified Epoxy Resin]

A carboxyl modified epoxy resin which has formed secondary hydroxylgroups in the molecule by previously reacting a part of epoxy groups inthe epoxy resin with e.g. a compound containing at least one carboxylgroup in the molecule can also be preferably used. In this case, thecarboxyl modified epoxy resin which has formed secondary hydroxyl groupsin the molecule can be obtained by reacting 0.01 to 0.6 equivalent ofcarboxyl group in the compound having at least one carboxyl group in themolecule, with 1 equivalent of epoxy group in the epoxy resin, in thepresence of a basic catalyst.

[Glycidyl Group- and Hydroxyl Group-Containing Radical Copolymer]

A radical copolymer having both glycidyl and hydroxyl groups in onemolecule, such as copolymers of glycidyl group-containing radicalcopolymerizable monomers such as glycidyl (meth)acrylate, hydroxylgroup-containing radical monomers such as hydroxyethyl (meth)acrylate,and other copolymerizable monomers can also be preferably used.

(b) Alkoxysilyl Group-Containing Compound

The alkoxysilyl group-containing compound (b) used in the presentinvention is represented by formula (2):

wherein R¹ represents a C1 to C8 alkyl group, a phenyl group or a C1 toC8 alkenyl group, each of which may have an alkoxy group, vinyl group,(meth) acryloyl group, carboxyl group, epoxy group, glycidyl group,amino group and mercapto group, R² represents a C1 to C8 alkoxysilylgroup, an alkyl group or a phenyl group, R³ represents a C1 to C8 alkylgroup, n is an integer of 0 to 6, and p is an integer of 0 to 2.Examples of the alkoxysilyl group-containing compound includetetraalkoxysilane such as tetramethoxysilane, tetraethoxysilane,tetrapropoxysilane, tetraisopropoxysilane and tetrabutoxysilane, andtrialkoxysilane such as methyltrimethoxysilane, methyltriethoxysilane,methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane,ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane,isopropyltrimethoxysilane, isopropyltriethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane,3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane,3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltiethoxysilane,3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,phenyltrimethoxysilane, phenyltriethoxysilane,N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane.

Partial condensation products of the above compounds can also bepreferably used.

(1-2) Method of Producing the Alkoxysilyl Group-Containing ModifiedEpoxy Resin

The method (1-2) of producing the alkoxysilyl group-containing modifiedepoxy resin includes, but is not limited to, methods of modificationdescribed in for example JP-A 2001-59011, JP-A 2002-249539 etc.

The method is carried out by introducing (a) epoxy resin containing atleast one hydroxyl group in one molecule and (b) alkoxysilylgroup-containing compound and reacting them under heating andsimultaneously distilling a byproduct alcohol away. The reactiontemperature is 50 to 130° C., preferably 70 to 110° C., and the totalreaction time is about 1 to 24 hours. This reaction is conducteddesirably under substantially water-free conditions so that thepolycondensation reaction of the alkoxysilyl group-containing compound(b) itself can be prevented from proceeding to a too high degree. In thede-alcohol condensation reaction, a conventionally known accelerator canbe used for promoting the reaction. The accelerator includes, forexample, organometallic compounds such as dibutyltin dilaurate and zincstearate.

The reaction can be carried out in a solvent or without a solvent. Thesolvent is preferably an organic solvent which is excellent in theability to solubilize (a) epoxy resin having at least one hydroxyl groupin one molecule and (b) alkoxysilyl group-containing compound and whichis inert to these compounds. Such organic solvent includes aproticsolvents, for example, ketone solvents such as methyl ethyl ketone andcyclohexanone, ester solvents such as ethyl acetate and butyl acetateand aromatic solvents such as toluene and xylene.

With respect to the ratio of (b) alkoxysilyl group-containing compoundto (a) epoxy resin having at least one hydroxyl group in one molecule,the hydroxyl equivalent of the epoxy resin (a)/alkoxysilyl equivalent ofthe alkoxysilyl group-containing compound (b) is preferably in the rangeof 0.01 to 0.5. An equivalent ratio outside of this range is notpreferable because when the equivalent ratio is less than 0.01, thealkoxysilyl group-containing compound in an unreacted form is increased,while when the ratio is higher than 0.5, sufficient heat resistancecannot be achieved. The unreacted epoxy resin component and theunreacted alkoxysilyl group-containing compound may be contained in thealkoxysilyl group-containing silane modified epoxy resin (1) thusobtained.

The modified state of the hydroxyl group-containing epoxy resin (a)modified with the alkoxysilyl group-containing compound (b) can beconfirmed for example with ¹H-NMR (CDCl₃ solution) by examining that amethine peak (in the vicinity of 3.3 ppm) of the epoxy ring ismaintained and a peak of hydroxyl group (in the vicinity of 3.85 ppm) inthe epoxy resin has disappeared.

The amount of the alkoxysilyl group-containing modified epoxy resin (1)in the liquid crystal sealing composition is contained preferably in anamount of 1 to 30% by weight based on 100% by weight of the liquidcrystal sealing composition. This range is preferable because the liquidcrystal sealing composition is superior in heat resistance andadhesiveness because of excellent viscosity stability and high Tg of itscured product.

(2) Heat Latent Epoxy Curing Agent

As the heat latent epoxy curing agent (2) used in the present invention,a known heat latent epoxy curing agent capable of conferring curingreaction on the epoxy resin upon heating can be selected and used.

Examples of the known heat latent epoxy curing agent include animidazole adduct-based curing agent, dicyandiamide modified curingagent, dicyandiamide, dihydrazide-based curing agent, imidazole-basedcuring agent, amine adduct-based curing agent, amine/acid anhydrideadduct-based curing agent, polyvalent phenol compound and acidanhydride-based curing agent etc.

The heat latent epoxy curing agent (2) desirably contains at least onekind of amine-based curing agent having a melting point or a softeningpoint (determined by a ring and ball method) of 100° C. or more. Theamine-based curing agent includes, for example, an imidazole-basedadduct curing agent, dicyandiamide modified curing agent,1,8-diazabicyclo(5,4,0) undecene-7 derivative, dicyandiamide,dihydrazide-based curing agent, amine based-adduct curing agent,imidazole derivative etc. The heat latent epoxy curing agent (2) used ismore preferably at least one kind of imidazole-based curing agent havinga melting point of 130° C. or more. Examples of the imidazole-basedcuring agent having a melting point of 130° C. or more include1-cyanoethyl-2-phenylimidazolium trimellitate (melting point 175° C. to183° C.), 2-phenylimidazole isocyanuric acid adduct (melting point 135°C.), 2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine (meltingpoint 248° C. to 258° C.) etc.

The heat latent epoxy curing agent (2) is contained in an amount of 2 to40% by weight based on 100 parts by weight of the liquid crystal sealingcomposition of the present invention. In this range, the curing of theliquid crystal sealing composition of the present invention issufficient, the Tg of its curing product and adhesiveness are excellent,and the viscosity stability of the composition at room temperature issuitable.

[Working Effect of the Amine-Based Curing Agent in a Pre-Cure Step inProduction of a Liquid Crystal Cell]

The alkoxysilyl group-containing modified epoxy resin (1) has, in itsmolecule, analkoxy group derived from the alkoxysilyl group-containingcompound (b). In a pre-cure step for producing a liquid crystal displaycell, it is preferable that the alkoxysilyl group-containing compound(b) in the liquid crystal sealing composition undergoes sol/gel curingthus substantially eliminating alcohol to make (1) substantially free ofthe alkoxysilyl group, in order to improve the outward appearance of theseal after attachment of panels. When the sol/gel curing of thealkoxysilyl group group-containing modified epoxy resin in the pre-curestep is insufficient, de-alcohol condensation reaction may, due to theresidual alkoxysilyl group in the seal, proceed in the step of heatingpress bonding with a sheet hot press, to cause a deterioration inoutward appearance due to foaming etc. in the seal. It is preferablethat the amine-based curing agent is present in the liquid crystalsealing composition, because de-alcohol condensation reaction can, dueto sol/gel curing, be promoted in the pre-cure step carried out usuallyat a temperature of 60 to 110° C. as described later, and thus after thepre-cure step, the alkoxy group is substantially not present. Further,this amine-based curing agent can also function as a curing agent forthe epoxy resin component in a subsequent heat curing step.

The heat latent epoxy curing agent (2) is preferably an imidazole-basedcuring agent having a melting point of 130° C. or more, from theviewpoint of excellent viscosity stability of the liquid crystal sealingcomposition of the present invention, the sol/gel curing of thealkoxysilyl group in the pre-cure step, and the curing of the epoxyresin component in a heat curing step.

(3) Filler Having an Average Particle Diameter of 0.1 to 10 μm

The filler (3) having an average particle diameter of 0.1 to 10 μm usedin the present invention may be any filler which can be usually used inthe field of electronic material. Specific examples include inorganicfillers such as calcium carbonate, magnesium carbonate, barium sulfate,magnesium sulfate, aluminum silicate, zirconium silicate, iron oxide,titanium oxide, aluminum oxide (alumina), zinc oxide, silicon dioxide,potassium titanate, kaolin, talc, asbestos powder, quartz powder, mica,glass fiber etc. Known organic fillers such as polymethyl methacrylate,polystyrene and copolymers thereof with copolymerizable monomers, andcore/shell type acryl particles can also be used.

Before use, the filler (3) maybe graft-modified with epoxy resin, silanecoupling agent etc.

The average particle diameter of the filler (3) used in the presentinvention is 0.1 to 10 μm, preferably 0.3 to 5 μm, as determined by alaser. An average particle diameter within this range is preferablebecause the dimensional stability of the width of a cell gap is furtherimproved in production of liquid crystal cells.

The amount of the filler (3) used in the present invention is preferably5 to 30% by weight, more preferably 10 to 20% by weight, based on 100%by weight of the whole liquid crystal sealing composition. It ispreferable that the amount of the filler used is in the above range,because the application stability of the liquid crystal sealingcomposition onto a glass substrate is excellent, and the dimensionalstability in the width of a cell gap is also excellent.

(4) Epoxy Resin Having at Least 1.2 Epoxy Groups on Average in OneMolecule

In the liquid crystal sealing composition of the present invention,epoxy resin not modified with alkoxysilyl can be used in combinationwith the alkoxysilyl group-containing epoxy resin (1). The epoxy resinused in combination is desirably epoxy resin having at least 1.2 epoxygroups on average in one molecule, preferably at least 1.7 epoxy groupson average in one molecule, particularly preferably 2 to 6 epoxy groupson average. When at least 1.2 epoxy groups on average are present in onemolecule, heat resistance is preferably improved. These epoxy resins maybe used singly or as a mixture of resins different from one another, andcan be used regardless whether they are solid or liquid at roomtemperature.

These epoxy resins are not particularly limited insofar as they areepoxy resin containing a predetermined amount of epoxy group or amixture thereof, and a mixture of a monofunctional epoxy resin and amultifunctional epoxy resin, a single multifunctional epoxy resin, or amixture thereof can be used. Modified epoxy resins thereof can also beused. The number of functional groups of the epoxy resin in the liquidcrystal sealing composition can be determined from the epoxy groupequivalent and weight-average molecular weight of the epoxy resinseparated by liquid chromatography. Examples of the epoxy resin (4)having at least 1.2 epoxy groups in one molecule include aliphaticglycidyl ether compounds, aromatic glycidyl ether compounds, trisphenolglycidyl ether compounds, hydroquinone glycidyl ether compounds,resorcinol glycidyl ether compounds, aliphatic glycidyl ester compounds,aromatic glycidyl ester compounds, aliphatic glycidyl ether estercompounds, aromatic glycidyl ether ester compounds, alicyclic glycidylether compounds, aliphatic glycidyl amine compounds, bisphenol glycidylether compounds, aromatic glycidyl amine compounds, hydantoin glycidylcompounds, biphenyl glycidyl compounds, novolak glycidyl ethercompounds, glycidyl group-containing (meth)acrylic copolymers,epoxylated diene polymers etc. Epoxy resin and modified epoxy resinother than those described above can also be simultaneously used.

[Modified Epoxy Resin]

As the epoxy resin (4) having at least 1.2 epoxy groups in one molecule,modified epoxy resin other than the alkoxysilyl group-containingmodified epoxy resin can also be mixed and used in such a range that thecharacteristics of the sealing composition of the present invention arenot deteriorated. Examples of the modified epoxy resin include urethanemodified epoxy resin, polysulfide modified epoxy resin, rubber modifiedepoxy resin (modified with CTBN, ATBN etc.), polyalkylene glycol epoxyresin, bisphenol A epoxy resin having ether elastomers added thereto,acryl modified epoxy resin etc. The liquid crystal sealing compositionof the present invention is particularly preferably the one having arubber modified product maintained as particles in the epoxy resin. Whenthese modified epoxy resins are simultaneously used, the stressrelaxation of the liquid crystal sealing composition may be improved toexhibit further improved adhesion.

(5) Aprotic Solvent Compatible with Epoxy Resin, Inert to an Epoxy Groupand Having a Boiling Point in the Range of 140 to 220° C.

To improve dispense coating properties and screen printing properties,the liquid crystal sealing composition of the present invention canemploy the aprotic solvent (5) compatible with epoxy resin, inert to anepoxy group and having a boiling point in the range of 140 to 220° C.

The amount of the aprotic solvent (5) inert to an epoxy group used inthe present invention is preferably 5 to 30% by weight based on 100% byweight of the liquid crystal sealing composition. An amount of thesolvent in the above range is preferable because the resultingcomposition is excellent in wetting properties on an adherent such as aglass substrate or the like and superior in dispense coating propertiesand screen printing properties.

The aprotic solvent (5) inert to epoxy resin is selected from solventscompatible with epoxy resin, inert to epoxy resin and having a boilingpoint in the range of 140 to 220° C. Specific examples include ketonesolvents such as cyclohexanone and methyl cyclohexane, ether solventssuch as diethylene glycol diethyl ether and diethylene dibutyl ether,and ester solvents such as propylene glycol diacetate and propyleneglycol methyl ether acetate. Use of a protonic solvent such as propyleneglycol methyl ether and dipropylene glycol methyl ether is notpreferable because the de-alcohol reaction of the alkoxysilylgroup-containing epoxy resin (1) is readily promoted during storage todeteriorate the viscosity stability of the liquid crystal sealingcomposition.

(6) Other Additives

In the present invention, additives such as an ion trapping agent, anion exchanger, a leveling agent, a pigment, a dye, a plasticizer and adefoaming agent can be used.

Method of Preparing the Liquid Crystal Sealing Composition

Preparation of the liquid crystal sealing composition is notparticularly limited, and involves suitably adding and mixing (1) analkoxysilyl group-containing modified epoxy resin, (2) a heat latentepoxy curing agent, (3) a filler having an average particle diameter of10 μm or less, and if necessary (4) an epoxy resin having at least 1.2epoxy groups on average in one molecule, (5) an aprotic solvent having aboiling point in the range of 140 to 220° C., compatible with epoxyresin and inert to an epoxy group, and (6) other additives. In thismixing, for example, the composition is kneaded by known kneadingmachines such as a two-arm stirrer, a roll kneader, a twin-screwextruder, a ball mill kneader etc., and finally the composition ischarged and sealed in a glass bottle or a plastic container afterdefoaming under vacuum.

Physical Properties of the Liquid Crystal Sealing Composition

The viscosity of the liquid crystal sealing composition before curing isnot particularly limited, but the viscosity at 25° C. by an E-typeviscometer is in the range of preferably 1 to 1000 Pa·s, more preferably5 to 500 Pa·s, still more preferably 10 to 200 Pa·s.

Method of Producing the Liquid Crystal Display Panel

The liquid crystal display panel of the present invention is produced byprinting or dispense-applying the liquid crystal sealing composition ofthe present invention on a site for constituting a bonding seal of asubstrate for glass or plastic liquid crystal cell, then pre-curing at60 to 110° C., registering it on another substrate to form a pair ofattached substrates, pressing the paired substrates under heating at 100to 160° C., and joining and fixing the paired substrates to a uniformthickness in the range of 2 to 7 μm. For bonding sealing with the liquidcrystal sealing composition by complete curing, it is necessary that theliquid crystal sealing composition is pre-cured to remove a methanolcomponent and volatiles completely from the liquid crystal sealingcomposition. General pre-curing conditions are selected such that thatthe temperature is in the range of 60 to 110° C., and the heating timeis 5 to 60 minutes. A higher pre-curing temperature is preferable forheating in a short time. The liquid crystal cell substrate usedincludes, for example, a glass substrate, plastic substrate etc. Amongthe substrates mentioned above, a glass or plastic substrate forconstituting a liquid crystal cell, which is provided with anorientation film represented by indium tin oxide, an orientation filmrepresented by polyimide, and another inorganic ion-shielding film innecessary regions, is used. The method of applying the liquid crystalsealing composition onto the substrate is not particularly limited, andthe liquid crystal sealing composition can be applied for example by ascreening printing coating method or dispenser coating method. Afterapplication, a pair of substrates are attached by pre-heating and joinedto each other by pressing, bonding and sealing under heating, and thethermal curing conditions are not particularly limited, and curing isconducted at about 100 to 160° C. for 0.5 to 24 hours.

In production with a sheet heat press in the heat press and bondingstep, the conditions of securing retention of a temporary gap are notparticularly limited, but preferably the liquid crystal display panel isproduced through two or more heating steps or aging steps wherein a pairof substrates are joined at 100 to 160° C. for about 2 to 10 minutes,then removed under relieved pressure, and completely cured and aged in aheating oven regulated at the same temperature.

The sheet heat press refers to a heat pressing machine which joins apair of substrates one after another, including a vacuum sheet heatpress such as a sheet heat press capable of heating under vacuum and arigid sheet heat press for forcibly heating, pressing and joining a pairsubstrates via a hot plate at the atmospheric pressure. Either sheetheat press system may be used. In addition to the sheet heat press, amulti-stage heat press can also be used in the heat press and bondingstep.

Liquid Crystal Display Panel

The liquid crystal display panel of the present invention is produced byprinting or dispense-applying the liquid crystal sealing composition ofthe present invention on a site for constituting a bonding seal of asubstrate for glass or plastic liquid crystal cell, then pre-curing at60 to 110° C., registering it on another substrate to form a pair ofattached substrates, pressing the paired substrates under heating at 100to 160° C., and joining and fixing the paired substrates to a uniformthickness in the range of 2 to 7 μm, and the liquid crystal displaypanel is a liquid crystal display element obtained by injecting a liquidcrystal material into the cell and sealing its injection hole with atwo-pack setting or UV-setting liquid crystal seal material composition.The two-pack setting or UV-setting liquid crystal sealing compositionmay be a known composition. The liquid crystal material is not limited,and a nematic liquid crystal and ferroelectric liquid crystal ispreferable.

Preferable examples of the liquid crystal display panel obtained in thepresent invention include a TN (twisted nematic) liquid crystal elementor STN (super twisted nematic) liquid crystal element proposed by M.Schadt and W. Helfrich or a ferroelectric liquid crystal elementproposed by N. A Clark and S. T. Lagerwall, or a liquid crystal displayelement having a thin film transistor arranged in each pixel.

EXAMPLES

Hereinafter, the present invention is described in more detail byreference to the Examples, but the present invention is not limitedthereto. The terms “%” and “parts” in the Examples refer to % by weightand parts by weight, respectively. The materials used in the Examplesare shown below.

[Test Method]

(Measurement of Glass Transition Temperature of Cured Liquid CrystalSealing Agent)

The liquid crystal sealing agent was applied to a thickness of 100 μm interms of cured product to form a thin film, then pre-cured at 90° C. for10 minutes and heat-treated at 120° C. for 60 minutes to form a curedproduct of about 100 μm in thickness. The dynamic viscoelasticity of thecured product was measured by Rheograph Solid L-1R manufactured by ToyoSeiki Seisakusho, at a frequency of 10 Hz and at an increasingtemperature of 5° C./min., and the peak-top temperature of loss tangent(Tan δ) was calculated and expressed as glass transition temperature(Tg)

(Bonding Sealing Test)

The liquid crystal display test panel produced via the sheet presscuring step under the conditions shown in Example 1 was observed under atest glass (magnification: ×20) to determine whether the seal line wasdisturbed or not and whether seal defects were caused due to defoamingin the seal.

(Adhesion Test)

This test was carried out according to JIS K6850. SUS304 was used asadherent. The liquid crystal sealing composition was applied onto anarea of 25 mm×10 mm in the adherent, and the resulting test specimen waspre-cured at 90° C. for 10 minutes, attached and fixed with a jig, andheat-treated at 120° C. for 60 minutes to prepare an adhesion testspecimen. Adhesive strength under shear was measured by a tensiletesting machine (Intesco [phonetic]). In the Examples, a test specimenshowing an excellent adhesion that is, an adhesive strength of 20 MPa ormore, was designated ◯, a test specimen showing a slightly inferioradhesion, that is, an adhesive strength of 10 to 20 MPa, was designatedΔ, and a test specimen showing an inferior adhesion, that is, anadhesive strength of less than 10 MPa, was designated x.

(Heat Resistant Adhesion Test)

An adhesion test specimen prepared in the same manner as in the adhesiontest was measured for its adhesive strength under shear in the samemanner as in the adhesion test under the condition of 120° C. In theExamples, a test specimen showing excellent adhesion, that is, anadhesive strength of 20 MPa or more, was designated ◯, a test specimenshowing slightly inferior adhesion, that is, an adhesive strength of 10to 20 MPa, was designated Δ, and a test specimen showing inferioradhesion, that is, an adhesive strength of less than 10 MPa, wasdesignated x.

(Adhesion Test)

An adhesion test specimen prepared in the same manner as in the adhesiontest was examined for its adhesive strength under shear in a pressurecocker test under the conditions of 121° C., 2 atmospheric pressure and100% humidity for 20 hours. In the Examples, a test specimen showingexcellent adhesion, that is, an adhesive strength of 20 MPa or more, wasdesignated ◯, a test specimen showing slightly inferior adhesion, thatis, an adhesive strength of 10 to 20 MPa, was designated Δ, and a testspecimen showing inferior adhesion, that is, an adhesive strength ofless than 10 MPa, was designated x.

[Used Materials etc.]

(1) Alkoxysilyl Group-Containing Modified Epoxy Resin

The alkoxysilyl group-containing modified epoxy resins in SynthesisExamples 1 and 2 below were synthesized and used.

Synthesis Example 1

In a four-necked flask equipped with a stirrer, a water separatorquipped with a condenser, a thermometer and a nitrogen inlet tube, 200 gmethyl ethyl ketone was added to 900 g bisphenol F epoxy resin(Epichlone 830S, epoxy equivalent 175/eq, manufactured by Dainippon Inkand Chemicals, Inc.), and then 5 gN-phenyl-γ-aminopropyltrimethoxysilane (trade name: KBM573, manufacturedby Shin-Etsu Chemical Co., Ltd.) was added thereto, and the mixture washeated to 60° C. and dispersed uniformly. 400 g tetramethoxysilane(trade name: KBM04, manufactured by Shin-Etsu Chemical Co., Ltd.) wasadded thereto, and further 1 g dibutyltin dilaurate (tradename: NeostanU-100, manufactured by Nitto Kasei Co., Ltd.) was added thereto, andwhile formed methanol was distilled away, the mixture was heat-treatedat 80° C. for 5 hours and then treated under reduced pressure at asimilar temperature, whereby methyl ethyl ketone was distilled away, andmethoxysilyl group-containing modified epoxy resin was produced. Theepoxy equivalent of the resulting methoxysilyl modified epoxy resin was305 g/eq.

Synthesis Example 2

In a four-necked flask equipped with a stirrer, a water separatorequipped with a condenser, a thermometer and a nitrogen inlet tube, 200g methyl ethyl ketone was added to 900 g hydroxy group-containingacrylic resin (Almatex PD 1700, epoxy equivalent 175/eq, hydroxylequivalent 1100 g/eq., manufactured by Mitsui Chemicals), and themixture was heated to 60° C. and dispersed uniformly. 200 gtetramethoxysilane (trade name: KBM04, manufactured by Shin-EtsuChemical Co., Ltd.) was added thereto, and further 1 g dibutyltindilaurate (trade name: Neostan U-100, manufactured by Nitto Kasei Co.,Ltd.) was added thereto, and while formed methanol was distilled away,the mixture was heat-treated at 80° C. for 5 hours and then treatedunder reduced pressure at a similar temperature, whereby methyl ethylketone was distilled away, and methoxysilyl group-containing modifiedepoxy resin was produced. The epoxy equivalent of the resultingmethoxysilyl modified epoxy resin was 916 g/eq.

(2) Heat Latent Epoxy Curing Agent

3-bis(hydrazinocarboethyl)-5-isopropyl hydantoin having a melting pointof 120° C. (trade name: Amicure VDH-J, manufactured by Ajinomoto) as ahydrazide curing agent,2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine(melting point of 248 to 258° C., trade name: Curezole 2E4MZ-A,manufactured by Shikoku Chemicals Corporation) as an imidazole curingagent, and xylylene phenol resin (trade name: Mirex XLC-LL (softeningpoint 76.5° C.) as a phenol curing agent were selected and used.

(3) Filler Having an Average Particle Diameter of 0.1 to 10 μm

Vikarox CR-10 [phonetic] (trade name) (average particle diameter 0.4 μm)manufactured by Vikousky [phonetic] was selected and used as amorphousalumina, and F351 (trade name) (average particle diameter 0.2 μm)manufactured by Zeon Kasei was selected and used as organic filler.MU-120 (tradename) (primary average particle diameter of 0.02 μm asdetermined by observation under an electron microscope) manufactured byShin-Etsu Chemical Co., Ltd was used as amorphous silica in theComparative Examples.

(4) Epoxy Resin

As the epoxy resin, bisphenol A liquid epoxy resin (trade name: EpomicR-140P; epoxy equivalent, 185 g/eq., manufactured by Mitsui Chemicals),o-cresol novolak epoxy resin (trade name: EOCN-1020-75; epoxy equivalent200 g/eq., softening point of 75° C., manufactured by Nihon Kayaku), andacryl rubber modified epoxy resin according to Synthesis Example 3 belowwere selected and used.

Synthesis Example 3 Synthesis of Acryl Rubber Modified Epoxy Resin

A 2000-ml four-necked flask equipped with a stirrer, a gas inlet tube, athermometer and a condenser was charged with 600 g bisphenol A epoxyresin (Epomik R-140P manufactured by Mitsui Chemicals) as liquid epoxyresin, 12 g acrylic acid, 1 g dimethyl ethanol amine and 50 g toluene,and the mixture was reacted at 110° C. for 5 hours to introduce doublebonds by introducing air. While nitrogen was introduced into thereaction system, 350 g butyl acrylate, 20 g glycidyl methacrylate, 1 gdivinyl benzene, 1 g azobisdimethyl valeronitrile and 2 gazobisisobutyronitrile were added thereto and reacted at 70° C. for 3hours and further at 90° C. for 1 hour. Then, toluene was removed at110° C. under reduced pressure, and the composition was rapidly cured atlow temperatures in the presence of a photo curing catalyst to giveacryl rubber modified epoxy resin having uniformly dispersed finecrosslinked acryl rubber particles having an average particle diameterof 0.05 μm as determined by measuring the dispersed rubber particlediameter by observing the morphology of a ruptured surface of the curedproduct under an electron microscope.

(5) Solvent

Propylene glycol diacetate (trade name: Dowanol PGDA, manufactured byDow Chemical) (melting point: 191° C.) was selected and used as theaprotic solvent compatible with epoxy resin, inert to an epoxy group,and having a boiling point in the range of 140 to 220° C.

Example 1

30 parts of xylylene phenol resin (trade name: Mirex XLC-LL,manufactured by Mitsui Chemicals) and 10 parts of o-cresol novolak epoxyresin (trade name: EOCN-1020-75, manufactured by Nippon Kayaku) wereadded to 15 parts of propylene glycol diacetate (trade name: DowanolPGDA, manufactured by Dow Chemical), and the mixture was heated anddissolved, and then 15 parts of the alkoxylsilyl group-containingmodified epoxy resin in Synthesis Example 1, 10 parts of the acrylmodified epoxy resin in Synthesis Example 3, 3 parts of Curezole 2E4MZ-Aand 17 parts of CR-10 as filler were preliminarily mixed with a mixerand kneaded until the size of the solid materials was reduced to 5 μm orless with a triple roll mill, and the resulting kneaded product wasdefoamed under vacuum to give a liquid crystal sealing composition (P1).

The liquid sealing composition (P1) exhibited an initial viscosity of 50Pa·s at 25° C. by an E type viscometer. The results of the joining sealtest of the liquid crystal sealing composition (P1), the glasstransition temperature measurement of the cured product, the adhesiontest, the heat resistant adhesion test, and adhesion test are shown inTable 2.

The joining seal test was carried out in the following manner. 5 partsof 5 μm short glass fiber spacer was blended with 100 parts of theliquid crystal sealing composition (P1), and the mixture wassufficiently mixed to give a vacuum-degassed composition. The resultingcomposition was first applied by a dispenser to form a patternconsisting of 4 cells of 1 inch per liquid crystal cell glass substrate(hereinafter, referred to as ITO substrate) provided with a transparentelectrode and an orientation film to give an ITO substrate having a sealcoating with a width of about 0.7 mm and a seal coating thickness ofabout 22 to 25 μm. Thereafter, the substrate was dried in a hot airdryer at 90° C. for 10 minutes, followed by placing and registeringanother ITO substrate on the substrate and subjecting the pairedsubstrates 10 times to primary joining sealing (pressure 0.03 MPa/cm²,160° C./6 min.) on a rigid sheet heat press manufactured by Joyo Kogaku.As a result, there was no sample having seal defects or a disturbed sealline attributable to generation of foam penetrating the seal, and everyliquid crystal display cell substrate thus produced had a desired cellgap of 5±0.1 μm.

Examples 2 to 5

According to the formulation in Table 1, the liquid crystal sealingcompositions according to the present invention were produced in thesame manner as in Example 1 and evaluated in the same manner as inExample 1.

Comparative Examples 1 to 3

Liquid crystal sealing compositions (C1 to C3) were produced in the samemanner as in Example 1 except that the alkoxysilyl group-containingmodified epoxy resin was not used, and a silane coupling agent componentwas used as an additive component, and the compositions were evaluatedin the same manner as in Example 1.

As is evident from the results in Table 2, it was confirmed that theliquid crystal sealing compositions of the present invention aresuitable for the sheet press heat bonding system and excellent inadhesion and heat resistance.

In Comparative Examples 1 to 3, on the other hand, the alkoxysilylgroup-containing modified epoxy resin is not used, and thus thecompositions are unsuitable for the sheet press heat bonding system andinferior in adhesion and heat resistance.

TABLE 1 Liquid crystal sealing composition Comparative Examples ExamplesComposition P1 P2 P3 P4 P5 C1 C2 C3 (1) Alkoxysilyl Synthesis 15 — 20 2528 — — — group-containing Example 1 modified epoxy Synthesis — 25 — — —— — — resin Example 2 (2) Epoxy resin Amicure — — 10 10 — — — heatlatent VDH-J curing agent Curezole 3 3 3 3 3 3 3 3 2E4MZ-A Mirex XLC-LL30 25 — — 34 35 35 30 (3) Filler MU-120 — — — — — 2 12 2 CR-10 17 16 2717 15 20 10 15 F351 — — — 10 (4) Epoxy resin Epomic R140P — 3 — 25 5 —10 15 having at least 1.2 EOCN-1020-75 10 — 15 — — 10 — — epoxy groupsin Synthesis 10 10 10 20 — 10 10 10 the molecule Example 3 (5) SolventDowanol 15 18 15 — — 15 15 5 Additive PGDA KBM403 — — — — 5 5 5 20 (1)Alkoxysilyl group-containing modified epoxy resin

Synthesis Example 1: Bisphenol F liquid epoxy resin modified withN-phenyl-3-aminopropyltrimethoxysilane and tetramethoxysilane

Synthesis Example 2: Glycidyl group- and hydroxyl group-containingacrylic copolymer modified with N-phenyl-3-aminopropyltrimethoxysilaneand tetramethoxy silane

(2) Epoxy Resin Heat Latent Curing Agent

Amicure VDH-J:

1,3-bis(hydrazinocarboethyl)-5-isopropyl hydantoin manufactured byAjinomoto

Curezole 2E4MZ-A:

2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine

Mirex XLC-LL: xylylene phenol resin manufactured by Mitsui Chemicals

(3) Fillers

MU-120: fine silica particles manufactured by Shin-Etsu Chemical

CR-10: amorphous alumina manufactured by Vikousky

[phonetic]

F351: core/shell acryl particles manufactured by Zeon Kasei

(4) Epoxy Resin having at Least 1.2 Epoxy Groups in the Molecule

Epomic R140P: bisphenol A liquid epoxy resin manufactured by MitsuiChemicals

EOCN-1020-75: o-cresol novolak epoxy resin manufactured by Nippon Kayaku

Synthesis Example 3: acryl rubber modified epoxy resin (5) Dowanol PGDA:propylene glycol diacetate manufactured by Dow Chemical

Additive

KBM403: γ-glycidoxypropyltrimethoxysilane

TABLE 2 Test results of liquid crystal sealing compositions ComparativeComparative Comparative Test Items Example 1 Example 2 Example 3 Example4 Example 5 Example 1 Example 2 Example 3 Liquid P1 P2 P3 P4 P5 C1 C2 C3crystal sealing composition Measurement 133 130 142 145 148 115 101 115results of glass transition temperature (° C.) of cured product Resultof joining seal test Disturbed absent absent absent absent absentpresent present present seal line Foaming in absent absent absent absentabsent present present present seal Sheet heat suitable suitablesuitable suitable suitable unsuitable unsuitable unsuitable presssuitability Results of ◯ ◯ ◯ ◯ ◯ Δ ◯ ◯ adhesion test Results of ◯ ◯ ◯ ◯◯ Δ X Δ heat resistant adhesion test Results of ◯ ◯ ◯ ◯ ◯ Δ X X adhesivetest

INDUSTRIAL APPLICABILITY

The liquid crystal sealing composition of the present invention isexcellent in adhesiveness, moisture permeation resistance and heatresistance and is thus useful as a sealing agent for display panel invarious instruments.

1. A one-component liquid crystal sealing composition comprising (1) analkoxysilyl group-containing modified epoxy resin obtained by de-alcoholcondensation reaction of (a) an epoxy resin having at least one hydroxylgroup in one molecule and (b) an alkoxysilyl group-containing compoundrepresented by formula (2):

wherein R¹ represents a C1 to C8 alkyl group, a phenyl group or a C1 toC8 alkenyl group, each of which may have a C1 to C8 alkoxy group, vinylgroup, acryloyl group, methacryloyl group, carboxyl group, epoxy group,glycidyl group, amino group and mercapto group, R² represents a C1 to C8alkoxysilyl group, a C1 to C8 alkyl group or a phenyl group, R³represents a C1 to C8 alkyl group, n is an integer of 0 to 6, and p isan integer of 0 to 2, (2) a heat latent epoxy curing agent and (3) afiller having an average particle diameter of 0.1 to 10 μm.
 2. Theone-component liquid crystal sealing composition according to claim 1,further comprising (4) epoxy resin having at least 1.2 epoxy groups onaverage in one molecule.
 3. The one-component liquid crystal sealingcomposition according to claim 2, wherein the alkoxysilylgroup-containing modified epoxy resin (1) is contained in an amount of 1to 30% by weight based on 100% by weight of the liquid crystal sealingcomposition.
 4. The one-component liquid crystal sealing compositionaccording to claim 2, wherein at least one kind of the heat latent epoxycuring agent (2) is an amine-based heat latent curing agent, and itsmelting point or its softening temperature as determined by a ring andball method is 100° C. or more.
 5. The one-component liquid crystalsealing composition according to claim 2, wherein at least one kind ofthe heat latent epoxy curing agent (2) is an imidazole-based curingagent having a melting point of 130° C. or more.
 6. The one-componentliquid crystal sealing composition according to claim 2, wherein thefiller (3) is contained in an amount of 5 to 30% by weight based on 100%by weight of the liquid sealing composition.
 7. The one-component liquidcrystal sealing composition according to claim 2, wherein (5) an aproticsolvent compatible with epoxy resin and inert to an epoxy group andhaving a boiling point in the range of 140 to 220° C. is contained in anamount of 5 to 30% by weight based on 100% by weight of the liquidcrystal sealing composition.
 8. A method of producing a liquid crystaldisplay panel, which comprises applying the one-component liquid crystalsealing composition of claim 2 on a sealing site of a liquid crystaldisplay panel and heat curing the composition.
 9. A liquid crystaldisplay panel produced by the method of producing a liquid crystaldisplay panel according to claim
 8. 10. The one-component liquid crystalsealing composition according to claim 1, wherein the alkoxysilylgroup-containing modified epoxy resin (1) is contained in an amount of 1to 30% by weight based on 100% by weight of the liquid crystal sealingcomposition.
 11. The one-component liquid crystal sealing compositionaccording to claim 1, wherein at least one kind of the heat latent epoxycuring agent (2) is an amine-based heat latent curing agent, and itsmelting point or its softening temperature as determined by a ring andball method is 100° C. or more.
 12. The one-component liquid crystalsealing composition according to claim 1, wherein at least one kind ofthe heat latent epoxy curing agent(2) is an imidazole-based curing agenthaving a melting point of 130° C. or more.
 13. The one-component liquidcrystal sealing composition according to claim 1, wherein the filler (3)is contained in an amount of 5 to 30% by weight based on 100% by weightof the liquid sealing composition.
 14. The one-component liquid crystalsealing composition according to claim 1, wherein (5) an aprotic solventcompatible with epoxy resin and inert to an epoxy group and having aboiling point in the range of 140 to 220° C. is contained in an amountof 5 to 30% by weight based on 100% by weight of the liquid crystalsealing composition.
 15. A method of producing a liquid crystal displaypanel, which comprises applying the one-component liquid crystal sealingcomposition of claim 1 on a sealing site of a liquid crystal displaypanel and heat curing the composition.
 16. A liquid crystal displaypanel produced by the method of producing a liquid crystal display panelaccording to claim 15.